As is well known, a fluid dynamic bearing device has features in, for example, its high speed rotation, high rotational accuracy, and quietness. Thus, the fluid dynamic bearing device is suitably used as a bearing device for a motor, such as for a spindle motor to be built in a disk drive such as an HDD, for a fan motor to be built in a PC and other devices, or for a polygon scanner motor to be built in a laser beam printer (LBP).
The fluid dynamic bearing device includes a radial bearing portion and thrust bearing portions, which are configured to support a rotating side in a radial direction and thrust directions, respectively. Recently, both the bearing portions are frequently made up of fluid dynamic bearings. The thrust bearing portions, each being made up of the fluid dynamic bearings (thrust bearing clearances thereof) are provided on both axial sides of a flange portion provided to one end of a shaft member (for example, FIG. 2 of Patent Literature 1) in some cases, and are provided on both axial sides of a bearing member fixed to an outer periphery of the shaft member (for example, FIG. 2 of Patent Literature 2) in some cases, and the like. In a fluid dynamic bearing device disclosed in Patent Literature 2, the flange portion provided to the one end of the shaft member in a fluid dynamic bearing device disclosed in Patent Literature 1 is omitted. Therefore, a configuration disclosed in Patent Literature 2 has an advantage in that the entire device can be compactified in an axial direction by an amount corresponding to the omission of the flange portion.
Incidentally, when the rotating side is supported by the thrust bearing portions each being made up of the fluid dynamic bearings, clearance widths of the thrust bearing clearances are required to be set and managed with high accuracy. Therefore, at time of assembly of the fluid dynamic bearing device (at time of assembly of members), the members are assembled while relative axial positions of the members involved in formation of the thrust bearing clearances is strictly managed. In the fluid dynamic bearing device disclosed in FIG. 2 of Patent Literature 2, a sealing member is fixed to a housing under a state of being axially engaged with a step portion formed on the housing. In this case, when the step portion is formed at a position that enables the two thrust bearing clearances to be set to predetermined clearance widths, it is considered that the clearance widths of the two thrust bearing clearances can be set easily with high accuracy only by fixing the sealing member to the housing under a state in which the sealing member is engaged with the step portion.